<?php
function distance( $lat1 , $lon1 , $lat2 , $lon2 ) { 
   $theta = $lon1 - $lon2 ; 
   $dist = sin ( deg2rad ( $lat1 )) * sin ( deg2rad ( $lat2 )) + cos ( deg2rad ( $lat1 )) * cos ( deg2rad ( $lat2 )) * cos ( deg2rad ( $theta )); 
   $dist = acos ( $dist ); 
   $dist = rad2deg ( $dist ); 
   $miles = $dist * 60 * 1.1515 ;
   return ( $miles * 1609.344 ); 
 }
?>